Double band presses (DE-OS 24 21 296) serve for continuous fabrication of endless web-shaped materials, especially for production of decorative layered material laminates, copper-coated electrolaminates, thermoplast webs, chipboards, fiberboards and the like. These double band presses have two endlessly revolving press bands, in between which the material web is cured with application of pressure and possibly also heat and simultaneous conveyance in the feed direction. For generation of the pressure acting upon the material web, the so-called isobaric machines of this species are equipped with pressure chambers, which are bounded by a pressure plate and the press band in the vertical direction and on the sides by sliding face or floating seals. The pressure is built up in these pressure chambers by fluid pressure agents, such as oil or compressed air. So as to supply heat to the commodity being pressed, it is known to design the reversing drums on the inlet side of the double band press so that they can be heated. This heats the press bands of the double band press when travelling over the heated reversing drums. Then the press bands convey the quantity of heat thus picked up into the region where the commodity to be pressed lying between the two press bands is subjected to area pressure, the so-called reaction zone, and they yield there their heat to the commodity to be pressed. Because of the limited heat capacity of the press bands this quantity of heat however in many cases is insufficient.
Elements conducting heat have become known from the DE-OS 33 25 578 by means of which additional heat can be transferred to the press bands in the region of the reaction zone. These elements conducting heat consist of a material with good heat conductivity and are arranged at the pressure plate in the double band press having a surface assuring good heat conduction contact. The other surface of the heat-conducting elements contact the inner sides of the press bands in the region of the reaction zone in a dragging manner. The pressure plates are heated to a higher temperature than the specified temperature of the reaction zone, so that a heat gradient is provided between the pressure plates and the press bands and a heat flow is directed from a pressure plate through the heat-conducting elements onto the press band. This additional heat is transmitted by the press band then to the commodity being pressed. With such an arrangement a cooling of the press bands is also possible, by cooling the pressure plate.
In order to heat the pressure plates in a double band press it is further known from the DE-OS 24 21 296 to machine channels configured as bores into the pressure plate through which a heated fluid medium flows. If the pressure plate is to be cooled then a cooled fluid medium is directed through these bores. Gases or vapors but also liquids such as thermal oil or cooling liquids are suitable to be used as fluid media. Water can for instance also be used as a cooling liquid. Such fluid media for heating or cooling the pressure plate are hereinafter referred to as "heat carrier agents".
A disadvantage in the known heat-conducting elements is that the heat transfer occurs from the heat carrier agent flowing in the bores of the pressure plate onto the pressure plate, from the pressure plate to the heat-conducting element, and from the heat-conducting element finally to the press band. Each individual heat transfer results in a diminution of the effective heat-conducting capacity. The considerable travel from the bore in the pressure plate up to the press band leads also to a limitation of the heat flow. In some application cases the maximum heat transmitted by means of the heat-conducting elements is insufficient.